Mosquitoes modified to only give birth to males in bid to wipe out malaria

Genetically modified mosquitoes could help stamp out malaria by preventing
biting females from being produced

Mosquitoes have been genetically modified so they only give birth to males in a new technique that scientists hope could help to wipe out malaria.

The disease is spread by female mosquitoes, which pass on the disease when they bite humans.

But researchers from Imperial College London have now tested a new method that introduces genetically modified mosquitoes to normal Anopheles gambiae mosquito populations, the main carrier of the malaria parasite.

The GM insects had been altered so that they would not produce female offspring.

In the first laboratory tests where the modified mosquitoes were mixed with normal insects, 95% of the eggs laid hatched into males.

It is hoped that if this could be replicated in the wild, the technique would ultimately cause the malaria-carrying mosquito population to die out within a few generations.

Dr Nikolai Windbichler, a lead researcher from the Department of Life Sciences at Imperial College London, said: "What is most promising about our results is that they are self-sustaining.

"Once modified mosquitoes are introduced, males will start to produce mainly sons, and their sons will do the same, so essentially the mosquitoes carry out the work for us."

Although scientists have bred infertile mosquitos before, this is the first time they have been able to manipulate the sex ratios of mosquito populations.

It is only the female mosquito that bites as it feeds on blood to get the protein it needs for their eggs.

The scientists introduced the genetically modified mosquitoes to five caged wild-type mosquito populations. In four of the five cages, this eliminated the entire population within six generations, because of the lack of females.

Malaria is one of Africa's deadliest diseases, killing on average one child every 60 seconds. Globally, there are more than 200 million cases per year and more than 650,000 deaths, mostly in African children under five.

Since 2000, increased prevention and control measures have reduced global malaria mortality rates by 42 per cent, but the disease remains a prevalent killer as mosquitoes become increasingly resistant to insecticides and malaria parasites resistant to drugs.

Dr Roberto Galizi from the Department of Life Sciences at Imperial College London, said: "The research is still in its early days, but I am really hopeful that this new approach could ultimately lead to a cheap and effective way to eliminate malaria from entire regions. Our goal is to enable people to live freely without the threat of this deadly disease.”

During the study, published in the journal Nature Communications, scientists inserted a DNA cutting enzyme called I-PpoI into Anopheles gambiae mosquitoes.

In normal reproduction, half of the sperm bear the X chromosome and will produce female offspring, and the other half bear the Y chromosome and produce male offspring.

The enzyme used by the researchers works by cutting the DNA of the X chromosome during production of sperm, so that almost no functioning sperm carry the female X chromosome.

As a result the offspring of the genetically modified mosquitoes was almost exclusively male.